I have tables with UTC dates. When trying to get the day of week by using dow in PostgreSQL, I get the wrong day if the hours flow to the next day (and I need the right dow).
I created a fiddle to show the problem:
http://sqlfiddle.com/#!15/9aa9e/11
If I run the queries locally on my pgAdmin, it will return the correct dow. But on fiddle and from rails, I get the wrong dow. Any ideas?
Ok, so I understood that pgAdmin does it's own dow magic based on my timezone, and when rails sends that, it obviously doesn't happen.
The system I work on relies on the fact that rails does it's conversion magic for UTC datetimes back and forth, which work great if you don't use local postgreSQL timezone related functions such as DOW. What I did not is that it worked fine if I gave the dow the right offset. So here's my solution to the problem if anyone else needs it:
utc_diff = Time.current.time_zone.utc_offset/60/60
# making sure the diff is either + or - (minus is automatic)
utc_diff = utc_diff < 0 ? utc_diff : "+#{utc_diff}"
dow_part = "EXTRACT(DOW FROM punches.punched_in_at at time zone 'UTC#{utc_diff}') as dow"
So there you have it, hope it helps others.
Related
I have the contract start of a number of companies, and I want to report on each contract year by creating a column with the contract start updated to a select year. There are a number of solutions in SQL involving functions like DATE_ADD or DATEFROMPARTS, but I'm having trouble adapting it to rails (if those functions are available at all).
The closest I've gotten is: Company.select("contract_start + '1 YEAR'::INTERVAL as new_contract_start"). This adds 1 year to each contract start but doesn't take into account contracts older than a year (or started the same year). I've also tried the following but again run into syntax errors:
new_year = 2020
Company.select("contract_start + '#{new_year} - EXTRACT (YEAR from contract_start) YEAR'::INTERVAL")
I'm looking for a solution that can either:
Directly set the year to what I want
Add a variable amount of years based on its distance from the desired year
I'm on Ruby 2.3.3
I think the key here was finding functions compatible with the PostgreSQL that my database was built on. Once I started searching for the functions I thought would help and their PostgreSQL equivalents, I found more compatible solutions, such as: NUMTODSINTERVAL in PostgreSQL
I ended up with:
contract_start_year = 2020
Company.select("contract_start + make_interval(years => CAST (#{contract_start_year} - EXTRACT (YEAR from contract_start) as INT))
I've also made it a bit smarter by adding the number of years required to get the latest contract date without going over the report date. This would be problematic if the report start date was "2020-01-01" but the contract start was "2017-06-01". Setting the contract date to "2020-06-01" would overshoot the intentions of the report.
report_start = "`2020-07-01`"
Company.select("contract_start + make_interval(years => CAST (EXTRACT (YEAR FROM AGE(CAST (#{start_quotations} AS DATE), contract_start)) AS INT)) as new_contract_year")
Note the additional single quotes in report_start since the SQL code need to read a string to convert it to a date
There might be other methods that can "build" the date directly, but this methods works well enough for now.
I already have InfluxDB working and getting monitoring data about some services (the value is just 1 for up and 0 for down). For the management I need to select the values from the database that are in a specific month and either night time or day time. For example: I want to select all the data from April 2019 (doesn't matter if it 1 or 0) between 08:00AM and 07:00PM (day time)
Here is what I've tried:
SELECT value FROM probe_success
WHERE "instance" = 'https://myservice/api' AND time >= '08:00:00' AND time < '19:00:00'
AND time >= '2019-04-01' AND time <= '2019-04-30'
But I've got an error:
{"results":[{"statement_id":0,"error":"invalid operation: time and
*influxql.StringLiteral are not compatible"}]}
Can anyone tell me what I'm doing wrong or point me in the right direction?
Thank you very much!
Ok, so after some research I've found that it is not possible to use the "OR" statement in a "WHERE" clause to specify multiple time ranges. See this. I solved this problem by sending separate requests for each day in a for loop and then concatenate all the results. It's not the best solution, I admit, but since they say it's not possible I guess this is the workaround.
I am using postrges db.
My domain has a date field:
java.util.Date requestedDate;
I am trying to search by date in my controller:
eq ("requestedDate", requestedDate)
This works fine, but the problem is that date and time has to be exactly matching for this. But in application the user will only enter the date to search items (like give me all requests which are made on 2014-02-05 and the browser application will add the current time to the request). So the comparison fails because the user entered time is different from the time during creation of the request.
I tried 'like' but it throws error.
How to compare only date part ?
You could do something like this:
Date now = new Date()
now.clearTime()
def results = Meeting.withCriteria {
between('date', now, now+1)
}
So this strips off the time portion of the current date, and then does a 'between' query (between midnight just gone and midnight 24 hours later).
Still it looks like there is no convenient way to realize this.
You need a small detour by computing the start of the day and the end of the day and use the between operator.
EDIT
I just saw now rcgeorge23 gave you the right example for doing this.
Sorry if that question sounds strange, but I'm diving into Rails and I'm still learning the jargon. Basically, I'm trying to create a single-pass query that uses the value of one of the model's attributes in a calculation in the query (assuming that's even possible).
I have a Tournament model that has a start_date attribute that is a DateTime object. I'm trying to create a query that returns all the Tournaments that have a start_date no older than 1 hour + the length of the tournament, or put another way, all tournaments that haven't yet started or have started, but haven't ended longer than an hour ago. My current query, which doesn't work, looks like this...
validTourneys = Tournament.where("start_date > (? - duration_in_mins)", (DateTime.now.utc - 1.hour))
where duration_in_mins is an integer attribute of the Tournament model, but this query doesn't work and it seems to be returning all the Tournaments all the time. I'd like to include duration_in_mins in the (DateTime.now.utc - 1.hour) part of the calculation, but I don't know how to reference it, which is why I included it in the string part of the query, hoping that would work. Am I at least on the right track?
I should mention I'm using SQLite for development and PostgreSQL for production.
Thanks for your wisdom!
The problem is that if you subtract minutes from a DateTime object, you are not subtracting minutes but days.
# This works as expected
dt = DateTime.now # Thu, 28 Apr 2011 09:55:14 +0900
an_hour_ago = dt - 1.hour # Thu, 28 Apr 2011 08:55:14 +0900
# But, this does not...
two_hours_in_minutes = 120
two_hours_ago = dt - two_hours_in_minutes # Wed, 29 Dec 2010 09:55:14 +0900
In the last example 120 days are subtracted instead of minutes. This is probably also happening in your query. You have to convert duration_in_minutes to days and then subtract.
I don't know enough about SQL to answer your question directly (I think this will probably also depend on what database you're using, so you might want to mention that).
Have you considered, though, having start_date and end_date as DateTime columns instead of start_date and duration_in_mins? If this is going to be a common query, that would certainly make it more performant, as well as making your code easier to read and understand.
This query will only work if your database is smart enough to know how to add (what I am assuming) is a DateTime and and integer. And I can't think of a database that will do that correctly the way you have it coded. No database will assume minutes. Some might do ticks, seconds, or days.
This part of the calculation
(? - duration_in_mins)
is going to happen on the database, not in Ruby-land.
I have a start/end times for a calculation I'm trying to do and am having a problem seeing if the end time is before 12AM the day after the start time. Also, I need to calculate how many days past the start time it is.
What I have: Start Date, End Date
What I need:
- How many 'Midnights' is the End Date past the Start Date?
Has anyone done anything like this?
This uses PHP 5.3, if you have an earlier version you may need to use unix timestamps to figure out the difference. The number of midnights should be the number of days difference assuming both start and end times have the same time. So setting both to be midnight of their current day setTime(0,0), should make the calculation correct.
Using the DateTime objects.
$start = new DateTime('2011-03-07 12:23:45');
$end = new DateTime('2011-03-08 1:23:45');
$start->setTime(0,0);
$end->setTime(0,0);
$midnights = $start->diff($end)->days;
Without using the setTime() calls, this would result in 0, because there is less than 24 hours between start and end. With the setTime() this results in 1 because now the difference is exactly 24 hours.
The diff() function was introduced in 5.3 along with the DateInterval class. In 5.2 you can still use the DateTime class but will have to work out the total days using the Unix timestamp.
$midnights = ($end->format('U') - $start->format('U')) / 86400
You can wrap that in an abs() function to the order of start/end does not matter.
Note: These functions may need to be tested for cases that involve DST.
A comment in the php date documentation uses round after dividing by 86400 (number of seconds in a day), to counter any issues that could be involved with DST.
An alternative approach with DateTimes would be to create them in the UTC.
$utcTimezone = new DateTimeZone('UTC');
$start = new DateTime('2011-03-07 12:23:45', $utcTimezone);
$end = new DateTime('2011-03-08 1:23:45', $utcTimezone);